The invention relates to customized surgical fixtures. Many types of surgical procedures rely on precisely guiding an instrument into the body. This is the case in stereotactic surgery in which a target point within a body, for example, within a brain, is identified in a three-dimensional scanned image of the body. A detailed survey of stereotactic surgery can be found in Textbook of Stereotactic and Functional Neurosurgery, P. L. Gildenberg and R. R. Tasker (eds.), McGraw-Hill, June 1997 (ISBN: 0070236046). In a typical approach to stereotactic surgery, a frame is attached to the body prior to scanning. After scanning, the target point in the body is identified in the scanned image with reference to the frame. Then, during surgery, an adjustable instrument guide is attached to the frame. The guide is adjusted to align with the target point. A related approach to stereotactic surgery is described in copending U.S. patent application Ser. 09/063,658 filed Apr. 21, 1998, which is incorporated herein by reference. In that approach applied to brain surgery, an adjustable instrument guide is attached directly to the skull. Once attached, it is adjusted to align with the target point.
These previous approaches to stereotactic surgery require adjustment of an instrument guide in order that the instrument can be driven accurately to the target point within the body.
Adjusting an instrument guide to align with a target point within the body can be complex and time consuming. In some procedures multiple points must be targeted. For example, in spinal sterotactic surgery, multiple targets on different spinal segments are used. In a general aspect of the invention, rather than targeting an adjustable instrument guide, a customized fixture is fabricated for a particular patient, such that targeting is unnecessary or greatly simplified. A fixed instrument guide attached to the customized fixture can be used to guide a surgical instrument to the desired point without adjustment.
In one aspect, the invention features a method for forming a surgical fixture for attaching to a body and providing a reference structure for precisely locating a target within the body, such as a particular point or an anatomical structure within the body. The method includes processing a three-dimensional scanned image of the body, for example a CT or MRI scan. The scanned image includes the target within the body, for example a point or region of the body, and a mounting location of the body. The method also includes determining a structure of the surgical fixture such that when attached at the mounting location of the body the fixture provides a reference structure in a determined location and orientation with respect to the target within the body.
The method can include one or more of the following features.
Multiple mounting points can be identified in the scanned image. The geometric relationship between corresponding mounting points on the fixture and the reference structure can then be determined. The method can further include attaching mounting anchors to the body prior to scanning the body. Scanning markers are attached to the anchors. The identified mounting points are then the locations of the scanning markers in the three-dimensional image.
The mounting location for the fixture can be an anatomical structure on the body. A contour of a surface of the fixture is determined to mate with the anatomical structure.
The method can include identifying the target in the scanned image. Also, a trajectory for reaching the target can be identified. The location and orientation of the reference structure is then determined with respect to the identified trajectory.
The structure of the fixture can be determined in terms of a solid model of the fixture which defines the volume enclosed by the surface of the fixture. The method can then also include fabricating the fixture according to the solid model.
The method can include attaching the surgical fixture to the body and guiding an instrument to the target with reference to the attached surgical fixture.
The method can include attaching the surgical fixture to the body and attaching multiple tracking markers to the surgical fixture. For example, the multiple tracking markers, such a light-emitting diodes, can be attached to a tracking fixture that is then attached to the surgical fixture. The method then includes tracking locations of the tracking markers relative to a remote sensing device, such as a camera array or a laser tracker. The method can further include tracking a location of a surgical instrument relative to the remote sensing device, for example by tracking locations of tracking markers attached to the instrument, and computing a relative position of the surgical instrument to the surgical fixture using the tracked location of the tracking markers and the surgical instrument relative to the remote sensing device.
The method can also include attaching a second surgical fixture at a second mounting location of the body, and attaching multiple tracking markers to the second surgical fixture. For example, the two surgical fixtures are attached at two mounting points on an articulated portion of the body, for example, on two bones coupled at a skeletal joint. The method then includes tracking locations of the tracking markers attached to the second surgical fixture relative to the remote sensing device and computing a relative position of the two mounting locations of the body from the tracked locations of the tracking markers attached to both surgical fixtures. For example, a configuration of a skeletal joint can be determined from the computed relative position of the mounting locations.
The body can include a spine and the mounting location can include a spinal segment. The method can also include forming a model of the spine. The method can further include forming a corrected model of the spine in a corrected configuration. The determined structure of the surgical fixture is such that when attached, the fixture provides a second reference structure in a determined location and orientation with respect to the target in the corrected configuration of the spine.
The method can include selecting a model of a standard fixture and deforming the model of the standard fixture in order to match the standard model to the target and the mounting location.
In another aspect, the invention features a surgical fixture formed from a computer model using a rapid prototyping and tooling technique. The fixture includes multiple mounting sections for attaching the fixture to a body at a predetermined mounting location on a body and a reference structure coupled to the mounting sections for guiding a surgical instrument into the body. When the fixture is attached to the body at the mounting location the reference structure is at a predetermined location and orientation to a target within the body. The fixture can include an instrument guide mounted on the reference structure for driving the instrument into the body.
In another aspect, the invention features software stored on a computer readable medium for causing a computer to perform the functions of processing a three-dimensional scanned image of a body, the scanned image including the target within the body and a mounting location of the body and determining a structure of a surgical fixture such that when attached at the mounting location of the body the fixture provides a reference structure in a determined location and orientation with respect to a target within the body.
Advantages of the invention include avoiding the need for targeting of an adjustable guidance fixture based on the location of target points within the body. This reduces the time required for surgery, and can increase the accuracy and precision of targeting.
Another advantage is that the customized fixture can provide a mounting base in a precise location relative to the body. This avoids a manual registration procedure of stereotactic surgery in which a correspondence between the scanned image and the physical body is established. The manual registration procedure can be time consuming and inaccurate.
Another advantage is that tracking markers, such as light sources or reflectors, can be attached at predetermined locations relative to the body, without requiring that mounting points, such as bone anchors, are in a particular configuration, and without requiring a manual registration step after the tracking markers are attached to the body. This provides flexibility in the choice of where to mount the fixture and reduces the time required before surgery can begin and provides improved accuracy compared to that typically achieved using manual registration and avoids errors inherent in a manual registration step.
Another advantage is that the customized fixture is easily attached to the body, for instance by mating the fixture to a set of anchors attached to the body prior to scanning, or in another instance, mating the fixture to the particular anatomy of the patient.
Another advantage is that the customized fixture can be repeatedly reattached to permanently implanted anchors in the body allowing follow-up or repeated procedures.
Another advantage of the invention is that the detailed fixture design can be based on a desired configuration of a configurable portion of the body, such as the spine, rather than solely on the configuration during scanning. This allows the fixture to be used not only to guide instruments into the body, but when attached to the body, to constrain the configuration of the body, such as correcting a spinal or orthopedic bone deformity or complex fracture.
Other features and advantages of the invention will be apparent from the following description, and from the claims.